The present invention relates to a spindle motor in which a rotor is supported at a stator by an air dynamic pressure bearing having a conical dynamic pressure bearing portion and a radial dynamic pressure bearing portion and a rotating device having the spindle motor as a driving source of a rotating body such as a magnetic disc, an optical disc, and a polygon mirror.
A rotating device using a spindle motor as a driving source of a polygon mirror such as, for example, an optical deflection device is disclosed in Japanese Opened Patent No. 60-208629 as shown in FIG. 12. The bearing of the spindle motor of the rotating device comprises an air dynamic pressure bearing portion 203 and a magnetic bearing portion 202. The air dynamic pressure bearing portion 203 comprises a convex side bearing member 207 having a truncated cone convex portion 207a and a concave side bearing member having a truncated concave portion 205 to which said truncated cone convex portion 207a is fitted without contact, and dynamic pressure generating grooves 208 such as herringbone are formed at the surface of said truncated cone convex portion 207a of the convex side bearing member 207. The concave side bearing member having the truncated concave portion 205 is a member in which a polygon mirror 201 is formed in one body and constitutes a main portion of a rotor. The convex side bearing member 207 having the truncated cone convex portion 207a is formed vertically at a base body 206 of a stator by a columnar attaching portion 201a. The magnetic bearing 202 is a suction type thrust magnetic bearing comprising permanent magnets 209 and 210 fixed respectively facing rotor side and stator side and supports the rotor including the polygon mirror 201 making float. A rotor magnet 211 is attached at the rotor including the polygon mirror 201, and a stator coil 213 is attached at a lower base body 212 facing the rotor magnet 211.
The above-mentioned optical deflecting device receives component of radial direction of air dynamic pressure generating at the air dynamic pressure bearing portion 203 to radial direction by forming the bearing comprising the air dynamic pressure bearing portion 203 and the magnetic bearing portion 202, and can rotate at high speed without contact smoothly and stably receiving magnetic suction force toward thrust direction by thrust direction component of air dynamic pressure generating at the air dynamic pressure bearing portion 203 to thrust direction. However, there has been a problem that supporting the shaft toward the radial direction is hard to be stable as the above-mentioned deflecting device is hard to miniaturize because it has the magnetic bearing 202 and radial dynamic pressure has only radial direction component of air dynamic pressure generating at the air dynamic pressure bearing portion 203.
In Japanese Opened Patent No. 2-173610, an optical deflection device has a spindle motor in which a rotor is supported at a stator by an air dynamic pressure bearing comprising at least the following tour components: a columnar bearing member in which radial dynamic pressure generating grooves are formed at an outer circumference face thereof; a cylindrical bearing member being a cylindrical member constituting a radial dynamic pressure portion in which the columnar bearing member is inserted rotatablly and constituting a part of a rotor; a first disk-shaped thrust member being a disk-shaped member in which a dynamic pressure generating grooves are formed at lower face thereof and constituting a first thrust dynamic pressure portion with upper end face of said cylindrical bearing member fixed at upper end portion of said columnar bearing member; and a second disk-shaped thrust member being a disk-shaped where dynamic pressure generating grooves are formed at upper face thereof and constituting a second thrust dynamic pressure portion with lower end face of said cylindrical bearing member fixed at upper end portion of said columnar bearing member.
As the optical deflection device disclosed in the Japanese Opened Patent No. 2-173610 is a rotating device having an air dynamic pressure bearing comprising one radial dynamic pressure bearing portion and two, upper and lower thrust dynamic pressure bearing portions, there is not any problem such as that it is difficult to miniaturize and it is unstable to support the shaft of radial direction in the rotating device disclosed in the Japanese Opened Patent No. 60-208629. However, because the air dynamic pressure bearing adopted in the prior rotating device needs at least four components: the columnar bearing member; the cylindrical bearing member; and two, upper and lower disk-shaped thrust members, parallelism of the two disk-shaped thrust members must be finished in high accuracy, working cost is high, and therefore, price of products is high. Moreover, as the disk thrust members are attached at upper and lower positions just before the motor stops or when the motor starts, sliding with contact which the rotor and the disk-shaped thrust member rub each other at wide area thereof appears so as to be a problem of shortening product life. Furthermore, there is a problem that smooth starting of the motor is obstructed because the rotor aid the disk-shaped thrust member are adhered to each other when the motor starts.
FIG. 13 shows an example of the prior spindle motor in which a rotor is supported at stator by an air dynamic pressure bearing having a conical dynamic pressure bearing portion and a radial dynamic pressure bearing portion. The air dynamic pressure bearing comprises a columnar bearing member 302 in which a conical convex portion 302a is formed at a lower end thereof and a columnar portion 302b is formed at an intermediate portion thereof, and a cylindrical bearing member 303 in which a conical concave portion 303a is formed at a bottom portion thereof and a cylindrical portion 303b at an intermediate portion thereof. The conical dynamic pressure bearing portion comprises the conical convex portion 302a and the conical concave portion 303a, and dynamic pressure grooves G thereof are formed at surface of the conical portion 302a at two, upper and lower stages. Moreover, said radial dynamic pressure bearing comprises the columnar portion 302b and the cylindrical portion 303b. Dynamic pressure grooves G thereof are formed at upper end of the columnar portion 302b in two, upper and lower stages, and at lower end thereof in two, upper and lower stages. The rotor includes a rotor member having a substantially cup-shaped hub construction and attached to rotor magnet 306, and is attached at said air dynamic pressure bearing fitting an attaching hole to the columnar end portion 302c of the columnar bearing member 302. The stator includes a base plate 301 and a stator coil 305. The cylindrical bearing member 303 is formed at the base plate 301 and the stator coil 305 is attached at outer circumference face of the cylindrical bearing member 303.
As the conical dynamic pressure bearing portion and the radial dynamic pressure bearing portion are located at upper and lower portions on the rotating shaft, namely thrust direction in the air dynamic pressure bearing, the whole bearing becomes long. Pressure distribution of the bearing at the air dynamic pressure bearing has three peaks on the rotating shaft or thrust direction as shown in FIG. 14 defining vertical axis as position and horizontal axis as pressure P. It needs for stability of rotation that gravity position of rotating body having the air dynamic bearing and center of pressure distribution of the bearing are kept so as to match. Because of the restriction of construction, the prior air dynamic pressure bearing shown in FIG. 13 is hard to miniaturize. There is a problem that inclination vibration is likely is easy to generate.
The problem to be solved by the present invention is to provide a spindle motor and a rotating device having the spindle motor as a driving source of a rotating body in which a rotor is supported at a stator by an air dynamic pressure bearing such that the number of components are few, miniaturization is possible, working is easy, sliding with contact just before stop or at start of motor is extremely decreased, and smooth start of motor is not obstructed.
Further, the problem to be solved by the present invention is to further improve stability of rotation by applying said air dynamic pressure bearing to load of larger thrust direction, by removing possibility of generation of inclination vibration, and by preventing undesirable moving to upper side of convex side bearing member in a spindle motor and a rotating device having the motor as a driving source of the rotating body having an air dynamic pressure bearing in which a radial dynamic pressure bearing portion and a conical dynamic pressure bearing portion are located at inside and out side in the same axis respectively.